Magnetic chuck



June 12, 1962 G. N. LEVESQUE MAGNETIC CHUCK Filed June 16, 1959 1722@#haar HMI United States Patent O 3,039,026 MAGNETIC CHUCK George N.Levesque, Warwick, RJ., assignor to Brown & Sharpe Mfg. Co., Providence,RJ., a corporation of Rhode Island Filed June 16, 1959, Ser. No. 820,7924 Claims. (Cl. 317-159) The present invention relates to magnetic chucksand more particularly to a magnetic chuck having a finely divided workholding surface `adapted for the holding of thin stock.

It is a principal object of the invention to provide an improvedmagnetic chuck in which the magnets and pole pieces together with themagnetic inserts and spacing elements of the chuck work holding plateassembly are so constructed and arranged las to provide a holdingsurface adapted for holding very thin stock which may be of as little as.001" to .001 in thickness with a greater degree of firmness andtenacity than heretofore considered possible.

It is another object of the invention to provide an irnproved magneticchuck of this general type having a finely divided magnetic surface inwhich the holding power provided by the magnetic flux acting upon thinstock is of a uniformly high strength over the entire work surface ofthe chuck.

With these and other objects in view, a feature of the inventionconsists in the improved construction and arrangement of the magnets,pole pieces, magnetic inserts, and spacer elements of a magnetic chuck`to provide for a very fine division of the magnetic areas andintervening nonconducting spaces together with an even distribution andmaximum flow ofthe magnetic ux over the entire surface.

More specifically, a feature of the invention consists in the provisionof a chuck having at least -two magnetic poles of opposite polarity,with work holding pole pieces sharply tapered from a root area ofmassive cross section at the underside of the work holding plateassembly to a small apex at the work face of the chuck, in combinationwith a series of downwardly tapered magnetic inserts together with theirintervening spacers, said magnetic inserts and the apex portions of saidpole pieces being so constructed and shaped as to provide a series ofsubstantially equal work holding magnetic areas over the entire workholding surface of the chuck including specifically those adjacent toand overlying said pole pieces.

With the above and other objects in view as may hereinafter appear theseveral features of the invention will be readily understood by oneskilled in the -art from the following description taken in connectionwith the accompanying drawings in which:

FIG. l is a plan View of a magnetic chuck embodying in a preferred formthe several features of the invention;

FlG. 2 is a sectional View in side elevation taken on a line 2 2 of FIG.l;

FIG. 3 is a somewhat fragmentary sectional view similar to FIG. 2 but onan enlarged scale illustrating my improved construction of the magneticwork holding surface of the chuck; and

FIG. 4 is a diagrammatic view on an enlarged scale of a pole piecetogether with adjacent magnetic inserts and spacers to illustrateparticularly the distribution of the flux from the pole piece into theadjacent magnetic spacers and into a workpiece mounted on the workholding surface of the chuck.

The invention is herein disclosed as embodied in a permanent magnetchuck of the general type having a roughly rectangular work surfacecomprised of a series of pole pieces spaced across the work holdingsurface,

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and a series of magnetic inserts and nonmagnetic spacers interposedbetween adjacent pole pieces to provide a holding surface having finelydivided magnetic holding areas adapted for holding thin stock. Adjacentpole pieces are oppositely polarized by means of magnets which cause aflux to flow between the pole pieces ythrough the interposed magneticinserts land across the many air gaps provided between the finelydivided adjacent magnetic surface holding areas of the chuck.

Referring particularly to the drawings, the illustrated chuck comprisesa circular casing 10 which may be of aluminum formed with a squarecutout 12 to receive a rectangularly shaped chuck body, and a base plate14 fastened to the casing 10 lby means of machine screws 16. The chuckybody comprises an inner casing of nonmagnetic material generallydesignated at 18 within which are mounted four rectangularly shaped polepieces 20, 22, 24 and 26 which are separated -by three magnets 28, 30and 32 which are cross magnetized and are so arranged as to cause thepole pieces 20 and 22 to have a north polarization and the pole pieces22 and 26 to have a south polarization. In the preferred embodiment ofthe invention shown, magnets of grain oriented barium ferrite areemployed. It will be understood that the invention is not limited to theparticular kind or shape of magnets employed and further thatelectromagnets may be substituted within the spirit and scope of theinvention ifso desired.

In order to provide for a uniformly fine division of the work holdingsurface and at the same time to insure an even flow of the magnetic fluxfrom one to another of the finely divided magnetic areas includingparticularly those disposed directly over the individual pole pieces,the individual pole pieces 20, 22, 24, 26 are each formed with a largeroot area which comprises the full cross-sectional area of theindividual pole piece. As shown in the drawings, the sides of each polepiece, as for example, the pole piece 22 is formed at its upper end withsloping sides 36, 38 which form a taper starting at the underside of thework holding plate assembly and terminating in an apex 40 of small areaat the work holding face of the chuck. The pole piece 24 is similarlyprovided with a tapered top portion comprising sloping sides 42, 44which terminate in an apex 46 of small area at the top face of the workholding surface.

The end pole pieces 20 and 26 of the magnet assembly are formed at theirupper ends with outwardly sloping inner faces 50, 52 respectively whichextend from the underside of the work holding plate assembly to an apex5'4, 56 providing a small surface area at the work holding face of thechuck.

The portion of the work holding plate assembly between the two polepieces 22, 24 is formed of a series of downwardly tapered magneticinserts 58 which are separated from one another and from the taperedfaces 38 and 42 of the pole pieces 22, 24 by means of thin nonmagneticspacers 60 which are of uniform thickness and which provide suitable airgaps between the magnetic areas provided by the tip portions of the polepieces 22, 24 and the magnetic inserts 58.

The portions of the work holding plate assembly extending between thepoles 22 and 20 and between the poles 24 and 26 are identical inconstruction with that portion of the work holding :surface abovedescribed and one another by identical amounts by means of said spacers60.

The approximate dimensions of the illustrated chuck are given asfollows: The three rectangular cross-magv netized grain oriented bariumferrite magnets 28, 30 and 32 are preferably about .5 thick, the twoso-ft steel pole pieces 22, 24 are approximately .3 thick, and the twoside pole pieces 20, 24 will be approximately .2 thick. The magneticinserts may, for example, have a thickness at the upper or butt end of.019" and a thickness at the bottom tip of the tapered portion thereofof .009. The length of each of the air gaps provided by the nonmagneticspacing members are each ten thcusandths of an inch in thickness. Thetotal air gap between adjacent polarized pole pieces is approximately.21. The dimensions above given while suitable for use in the small tinemesh chuck illustrated utilizing grain oriented barium ferrite magnets,may be varied over wide limits in accordance with the work requirements,and will depend also on the magnetic source employed. It will beunderstood that the invention is not limited to the construction shownand that substantial variations may be employed both in the'pattern andsize of the magnets, and in the number and width of the magnetic insertsand spacers employed depending upon the use to which the chuck is to beput. In general, the beneiits of my invention will be realized mostfully when at least iive or more such magnetic inserts are employedbetween adjacent magnet poles. In a magnetic chuck particularly adaptedfor the holding of very tine work pieces which may be in the order of.001 to .002 or more in thickness, a very tine division of the chuckwork holding surface is to be desired.

My improved chuck work holding plate assembly hav- 'ing as componentparts thereof the tapered pole pieces and correspondingly taperedmagnetic inserts above described provides for a substantial increase involume and for a more eflicient distribution of the flux channeledthrough the magnetic work holding surface and through the work pieces tobe held thereby, particularly thin stock. It will be understood that forthe holding of thin stock such as indicated at 64 in FIG. 4 asubstantially uniform distribution of flux over the nely dividedmagnetic work holding surface is essential since a massive concentrationof ilux at any particular point on the work holding surface, will resultmerely in the passage of the flux through the thin work without anysubstantial holding effect. In particular, my tapered pole piececonstruction provides a massive root area through which the entireamount of the flux generated by the magnetic source is readily channeled(see FIG. 4) across the magnetic inserts and intervening nonmagneticspacers to another tapered pole piece which is similarly formed with amassive root area of suicient extent to channel the entire amount of theflux generated back to the magnetic source. With this arrangement amaximum amount of flux will be channeled through the upper or apexportion of the tapered pole piece 40 and through the interveningmagnetic inserts and nonmagnetic spacers to the -apex portion 46 of thenext adjacent pole piece of opposite polarity, so that each of themagnetic areas including Iboth the magnetic inserts and the apexportions of the individual pole pieces will receive substantially thesame volume of magnetic flux and thus will form a very large number ofmagnetic holding circuits from one magnetic area to another across theintervening nonmagnetic spacers.

The invention having been described what is claimed is:

1. In a magnetic chuck having -a magnetic iiux generating means, thecombination of a work holding assembly which comprises pole pieces ofopposite polarity, cach of said pole pieces having a root area at theunderside of said work holding plate assembly of substantial crosssection sufficient for carrying a large proportion of the flux generatedby said flux generating means and a tapered portion projecting `upwardlyfrom said root portion through the work holding plate assemblyterminating in a small apex `forming a portion of the work holdingsurface of said working holding plate assembly, and interposed betweensaid pole pieces a series of downwardly tapered magnetic insertsproviding a series of magnetic holding areas in the surface of said workholding plate assembly, and nonmagnetic spacers disposed between andseparating each of said magnetic inserts and pole pieces from oneanother to provide magnetic flux circuits of substantially uniformmaximum strength and tenacity between adjacent magnetic holding areasacross the width of said Work holding assembly.

2. In a magnetic chuck the combination with a magnetic ux generatingmeans of a work holding plate assembly comprising at least two magneticpole pieces of opposite polarity connected with said flux generatingmeans, each of said pole pieces having a root area at the underside ofsaid work holding plate assembly of substantial cross section sufficientfor carrying a large proportion of the flux generated by said fluxgenerating means and a tapered portion projecting from said root portionupwardly through the work holding plate assembly and terminating in asmall apex forming a portion of the work holding surface of said workholding plate assembly, and interposed between said pole pieces a seriesof downwardly tapered magnetic inserts, and nonmagynetic spacersdisposed between and separating each of said magnetic inserts and polepieces from one another, said magnetic inserts and the apex portions ofsaid pole pieces being so constructed and arranged as to provide in saidwork holding surface a series of holding magnetic areas of substantiallyequal width whereby lines of flux of substantially equal density aredirected from one to another of said magnetic areas comprised by saidpole pieces and magnetic inserts.

3. In a magnetic chuck, the combination of work holding plate assemblycomprising at least two polarized pole pieces of opposite polarity eachhaving a iiux carrying root area at the underside of said work holdingplate assembly of substantial cross section tapered upwardly to a smallapex forming a surface magnetic holding area in said work holding plateassembly, and interposed between said polarized pole pieces, a series ofat least `five downwardly tapered magnetic inserts providing interveningmagnetic holding areas of said work holding plate assembly, and meansproviding nonmagnetic gaps of substantially yuniform thickness betweeneach of said tapered magnetic inserts and said polarized tapered polepieces, the surface magnetic holding areas of said polarized pole piecesand magnetic inserts being so constructed and arranged as to provide aseries of holding surface magnetic areas of substantially uniform widthto provide magnetic flux circuits of substantially uniform strength andtenacity between adjacent magnetized holding areas along lines projectedfrom one to the other of and including the apexes of said polarized polepieces.

4. In a magnetic chuck the combination wtih magnetic ilux generatingmeans, of a work holding plate assembly comprising a plurality of polepieces of alternating polarity connected with said magnetic uxgenerating means and spaced from one another across said work holdingplate assembly, each of said pole pieces having a root area at theunderside of said Work holding plate assembly of a substantial crosssection suiiicient for carrying a maximum flux `generated by saidmagnetic flux generating means, and a tapered portion adjacent to saidroot area tapered upwardly to a small apex forming a portion of thesurface area of said work holding plate assembly, and in each of thespaces provided between adjacent pole pieces a series of downwardlytapered magnetic inserts and nonmagnetic spacers separating each of saidmagnetic inserts and pole pieces from one another, the butt ends of saidtapered magnetic inserts and the apexes of said polarized pole piecesappearing as magnetic holding areas in the surface of said work holdingplate assembly in, L..

to provide substantially uniform magnetic flux circuits of maximumstrength and tenacity between adjacent magnetized holding areas acrossthe Width of said Work holding assembly.

References Cited in the tile of this patent UNITED STATES PATENTS1,254,664 Downes et al Jan, 29, 1918 6 Hitchcock July 23, 1946 SimmonsJan. 25, 1955 Smit et al Jan. 13, 1959 Anderson et al Apr. 14, 1959FOREIGN PATENTS Great Britain July 13, 1949 Belgium Sept. 27, 1954

